Controlled dissection of a body lumen wall is a necessary treatment component of many widespread medical conditions. For example, in order to bypass a chronic total occlusion (CTO) in the vascular system, the physician can use a catheter to enter and travel through a length of the blood vessel wall corresponding to the site of the occlusion. As another example, one course of treatment for venous reflux involves modification of the blood vessel wall to create a valve and/or valve leaflet and/or repair a faulty valve and/or valve leaflet. One method for autologous creation of a valve leaflet, for instance, includes accessing the treatment site (either surgically or intravascularly) and entering the vessel wall with a catheter to create a dissection pocket (e.g., a portion of a body lumen wall where the wall has been separated into two or more distinct layers). Depending on the procedure (e.g., bypassing a CTO, creating a leaflet, etc.), it can be advantageous to finely control the shape and size of the dissection pocket. Such control can be challenging, especially considering the thinness and fragility of most body lumen walls, the presence of pathologic changes to body lumen walls, the curvature of most body lumen walls, and the effects of local, dynamic blood flow. Accordingly, the devices, systems, and methods of the present technology address these challenges.